Steel making converter

ABSTRACT

A bottom-blow converter for use in refining pig iron to make steel comprises a steel jacket with a refractory lining and an inserted bottom containing blowing nozzles. Each of the blowing nozzles is arranged to blow a jet of oxygen surrounded by a sheath of jacket gas into the melt. The nozzles are all circumferentially inclined in the same direction as each other with respect to the longitudinal axis of the converter and they are so arranged that the jets of oxygen and jacket gas which issue from them cause the melt to circulate both about the upright longitudinal axis of the converter and about a horizontal axis normal to this longitudinal axis so that the movement of the melt is the resultant of these two components of movement.

United States Patent 1 111] 3,774,893

Knuppel et al. Nov. 27, 1973 [54] STEEL MAKING CONVERTER 567,686 1/1933 Germany 266/35 [75] Inventors: Helmut Knuppel; Karl Brotzmann, 1 $2222" 266/35 both O S"1Zbah-R0Se"berg 609:558 2/1935 Germany 266 35 Georg Fassbinder,

Sulzbach-Rosenberg, all of Germany Primary Examiner-.l. Spencer Overholser Assistant Examiner-John E. Roethel [73] Assignee: Eisenwerke-Gesellschaft Atwmey Lawrence J Field Maximillianshutte mbH, Sulzbach-Rosenberg Hutte,

Germany v [57] ABSTRACT [22] Filed: Dec. 28, 1970 v [21] APPL No; 101,637 A bottom-blow converter for-use in refining pig iron to make steel comprises a steel jacket with a refractory lining and an inserted bottom containing blowing Foreign Application Priority Data nozzles. Each of the blowing nozzles is arranged to Dec. 27, 1969 Germany P 19 65 057.8 blow a jet of oxygen surrounded by a sheath of jacket gas into themelt. The nozzles are all circumferentially [52] U.S.'C1. 266/35 inclin d in the same direction as each other 'with re- [51] C2lc 5/48 spect to the longitudinal axis of the converter and they [58] Field of Search 266/36 P, 35 are so arranged that the jets of oxygen and jacket gas which issue from them cause the melt to circulate [56] References Cited both about the upright longitudinal axis of the con- UNITED STATES PATENTS verter and about a horizontal axis normal to this longi- 520,631 5/1894 Bull 266/36 P mdma] axis that the mmemem of the melt is the resultant of these two components of movement.

FOREIGN PATENTS OR APPLICATIONS 2,002,577 10/1969 France 1 Claim, 5 Drawing Figures PAH-TNTHJHMP? I973 3,774,893

sum 1 GF 3 FIG. 2

HELMUT KN'LFPPEL I KARL BROTZMANN HANS GEORG FASSBINDER INVENTORS STEEL MAKING CONVERTER In our prior Application Ser. No. 800,892 filed Feb. 20, 1969, now U.S. Pat. No. 3,706,549, granted Dec. 19, 1972, we have described a process for refining pig iron to make steel in a converter and in the process claimed a jet or jets of oxygen are blown into the melt to be refined through a nozzle or nozzles situated beneath the surface of the melt, the jet or each jet of oxygen being surrounded as it issues from its nozzle by a sheath of a jacket gas or vapour which is either inert or is slow to react with the melt and/or with the material of which the nozzle or nozzles are constructed.

This process has been applied on a large scale recently and has made it possible for the first time to revfine pig iron in a bottom blow converter using pure oxygen, to make steel. The particular advantages of the process are that very little iron is burnt away, and consequently very little brown smoke is produced.

The process can be controlled extremely precisely. It can be used for refining either Basic Bessemer steel or steel-making pig iron. To obtain low sulphur and low phosphorus contents in the steel, lime dust can be added to the jet of oxygen. In all cases the steel coritains very little nitrogen. A further advantage of the process is that the converter has'its working life considerably extended. The process is therefore very economical.

Finally, the pure oxygen is utilised very efficientlyf considerably raising the temperature of the melt during the process of refining. The blow periods may be shorter than they are in comparable processes. The proportion of scrap which may be added to the charge is increased, thus increasing the output of the converter.

The process in accordance with our prior Application is preferably effected in a converter in which a major part of the converter bottom is free from nozzles, the nozzles being installed mainly on one side of the bottom. This produces a positively directed circulation of the melt, the gases issuing from the nozzles giving a gas lift effect, so that the melt rises vertically, .is deflected downwards again at its surface and then moves downwards towards the part of the converter bottom free from nozzles. A continuous circulation of the melt thus takes place, the melt circulating about a horizontal axis, that is an axis normal to the longitudinal axis of the converter. The melt and slag are well mixed together, concentration equilibrium is rapidly obtained and the diffusion paths are short.

Although the process itself is practically independent of the pig iron composition, nevertheless towards the end of the blow a foamy slag may form and this splashes out when the converter is tipped. A number of methods are used, in the Basic Bessemer process for preventing the formation of foam in the silicate-rich slag which occurs at the beginning of the carbon removal. For example lime, dolomite or soda ash can be added to the melt in the form of small sized pieces.

The object of the present invention is to prevent the splashing out of slag which may occur during the last phase of the refinement in the process described and claimed in our prior Application.

To this end, according to the invention, in the pro cess claimed in our prior Application, the melt is caused to circulate both about the longitudinal axis of the converter and about a horizontal axis normal to the Ill 2 longitudinal axis, the movement of the melt being the resultant of these two components'ofmovement;

It has been found that the provisionof theextra component about the longitudinal axis of the converter largely suppresses the formation of foam towards the end of the blowing period. During the entire blowing process the refining of the melt proceeds very quietly and smoothly.

The additional component of movement of the melt may best be provided by using a converter which, in accordance with another aspect of the invention includes a steel jacket with a refractory lining and an inserted bottom with blowing nozzles each arranged to blow a jet of oxygen surrounded by a sheath of jacket gas,'the nozzles all being circumferentially inclined in the same direction with respect to the longitudinal axis of the converter. Preferably all the nozzles have their axes-inclined at the same angle of for example l5to a plane containing the longitudinal axis of the converter and intersecting the nozzle axis. I

An excellent circulation of the melt is obtained by ar: ranging the outlet openings of the n'ozzles on an'arc of a circle,.preferably on a semi-circle, centered on the longitudinal axis of the converter.

In vertain applications it is desirable to arrange the converter symmetrically, so that it can be tipped towards either side to empty it; This is required in particular in those cases where the steel is poured on one side of the converter and the slag on the other. A: converter of this kind is in the form of a body of rotation. The nozzles are'usually arranged in a row along-the'diameter of the converter bottom extending parallel toits tipping axis. In order to cause the melt "to circulate around'the longitudianl axis of the converter, in-accordancewith a further feature of the invention, the outlet openings of the nozzles are arranged in two parallel rows one on each side of the longitudinal axis of the converter.

The nozzles need not necessarily all be inclined at the same angle with respect to the converter axis, on the contrary, it may in some cases be preferable to give the nozzles nearer to the converter longitudinal axis a lesser inclination and the nozzles further away a greater inclination with respect to the axis, because the nozzles further away from the converter axis are more effective in producing the desired horizontal component of circulation of the melt.

Two examples of processes and of converters inaccordance with the invention will now be described-with reference to the accompanying drawings, in which:

FIG. 1 is a horizontal cross-section through one example of the converter asseen in the direction of' the arrows on the line I I in FIG. 2;

FIG. 2 is a vertical section through the first example as seen in the direction of the arrows on the line II II in FIG. 1;

FIG. 3 is a horizontal section through the second example of the converter as seen in the direction of the line III III in FIG. 4;

FIG. 3A is a simialr view showing a modification drawing. The converter has an inserted bottom 8 mounted on a detachable bottom plate 7. The longitudinal axis of the converter is indicated at 1 1. In the first example the bottom has a number of nozzles 10 each arranged to blow a jet of oxygen surrounded by a sheath of jacket gas. The gases are supplied from annular feeders, that for the oxygen having the reference numeral 9. The nozzles are all inclined circumferentially to give the melt in the converter a rotation about the longitudinal axis 11, that is to say the longitudinal axis of each nozzle lies at an angle to a vertical radial plane which contains the converter longitudinal axis 11 and intersects the nozzle axis. The inclination of the nozzles, that is to say the angle formed with this plane is preferably 15.

In the first example, the outlet openings 14 of the nozzles 10 are situated on a semi-circular are 15. The slanting attitudes of the nozzles ensure that the melt in the converter is given a rotation in the direction of the arrows 16. This rotary motion is superposed on a vertical circulation about a horizontal axis normal to the axis 1 1, represented by the arrow 17. The rotatary motion of the molten metal and slag about the axis 11 prevents foaming and splashing.

In the second example shown in FIGS. 3 and 4, which is symmetrical, that is to say a body of rotation, so that it can be tipped in either direction to empty it, there are nozzles with outlet openings 21 arranged in two rows 18 which are parallel but staggered with respect to each other. The lower ends of the two rows of nozzles are situated on both sides of a central gas manifold 24 for supplying oxygen and there are two manifolds for supplying jacket gas. All the nozzles have the same circumferential inclination, that is to say they all lie at the same angle to a vertical plane containing the longitudinal axis 1 1 and intersecting the axes of the two rows of nozzles symmetrically. The two rows of nozzles slant in opposite directions thus causing melt in the converter to circulate as indicated by the arrow 27, about the longitudinal axis.

This movement in the melt is superimposed on a vertical circulation about a horizontal axis normal to the axis 11 represented by the arrows 25, 26. The velocity of movement in the melt is determined by the slopes of the nozzles 20, by the depth of melt in. the converter and by the gas pressures forcing the oxygen and jacket gas through the nozzles. By adjusting the gas feed presures it is possible to control the velocity of horizontal movement in the melt.

In the modification shown in FIG. 3A the nozzles nearer to the convertor longitudianl axis have a lesser inclination and the nozzles further away have a greater inclination with respect to the axis, because the nozzles further away from the convertor axis are more effective in producing the desired horizontal rotational component of circulation of the melt, as noted above.

The process in accordance with the present invention possesses all the advantages of the process described in our prior Application. Moreover the process in accordance with the present invention can be controlled so that no splash-out occurs, even when the slag composition and melt temperature are particularly unfavourable from this point of view.

We claim:

1. In a bottom-blow converter for refining a bath of pig iron to make steel, said converter including a symmetrical steel jacket, a refractory lining in said steel jacket, an inserted bottom in said jacket and a plurality of blowing nozzles in said inserted bottom each of said nozzles having means defining two concentric passages, whereby each of said nozzles is adapted in use to blow a jet of oxygen surrounded by a sheath of protective fluid into said bath, the improvement wherein all of said nozzles are inclined in the same direction with respect to the longitudinal central axis of said converter, wherein each of said nozzles includes means defining an outlet opening and said outlet openings of all said nozzles are arranged in two parallel rows, one row being situated on each side of said longitudinal axis and extending parallel to the tilting axis of the converter and the nozzles nearer to said longitudinal axis have a relatively lesser inclination and the nozzles further away from said axis have a greater inclination with respect to the longitudinal axis. 

1. In a bottom-blow converter for refining a bath of pig iron to make steel, said converter including a symmetrical steel jacket, a refractory lining in said steel jacket, an inserted bottom in said jacket and a plurality of blowing nozzles in said inserted bottom each of said nozzles having means defining two concentric passages, whereby each of said nozzles is adapted in use to blow a jet of Oxygen surrounded by a sheath of protective fluid into said bath, the improvement wherein all of said nozzles are inclined in the same direction with respect to the longitudinal central axis of said converter, wherein each of said nozzles includes means defining an outlet opening and said outlet openings of all said nozzles are arranged in two parallel rows, one row being situated on each side of said longitudinal axis and extending parallel to the tilting axis of the converter and the nozzles nearer to said longitudinal axis have a relatively lesser inclination and the nozzles further away from said axis have a greater inclination with respect to the longitudinal axis. 